The present invention relates to a novel magnetoresistive effect head and a magnetic recording and reproducing apparatus using the same, and more particularly to a magnetoresistive effect head suitable for a recording head for reproducing information of a magnetic recording medium by utilizing a giant magnetoresistive effect and a magnetic recording and reproducing apparatus using the same.
A reproducing head as well as a recording head are mounted on a magnetic recording and reproducing apparatus, and an AMR (Anisotropic Magnetoresistive) head which utilizes an anisotropic magnetoresistive effect has been proposed as a reproducing head. In the AMR head, since it is required to suppress a Barkhausen noise generated by the head to prevent a malfunction of the magnetic recording and reproducing apparatus, a magnetic domain control layer for maintaining the magnetoresistive effect layer in a single magnetic domain state is provided in the head.
In a first generation AMR head having the magnetic domain control layer provided therein, a magnetic domain control system called a patterned exchange system as disclosed in U.S. Pat. No. 4,663,685 is adopted. In this system, a magnetic domain control layer formed of an antiferromagnetic film is patterned, the patterned magnetic domain control layer is stacked only in end regions of a magnetoresistive effect film (MR film), this region is maintained in a single magnetic domain state, and a central magnetic sensing area (a region sandwiched between a pair of electrodes for transducing a change in a magnetic field to an electrical signal) of the MR films is induced to a single magnetic domain state.
It has been reported that the AMR head adopting the patterned exchange system can improve a sensitivity by increasing a spacing of the magnetic domain control layers to be larger than a spacing of electrodes, as disclosed in N. Miyamoto et al., xe2x80x9cTrack Profile Characteristics of MR Heads with an NiO Domain Control Layer, Journal of the Magnetics Society of Japan, Vol. 19, No. 2, pp. 105-108 (1995) (in Japanese).
In a second generation AMR head, a hard biasing system is adopted as disclosed in JP-A-3-125311 in order to facilitate the manufacture as compared with the first generation AMR head. In this system, both ends of the MR film extended to the end regions are cut off, the MR film is formed only in the magnetic sensing area, and the magnetic sensing area is maintained in a single magnetic domain state by a magnetic field generated by a permanent magnet. It has also been proposed to use a lamination of ferromagnetic films and antiferromagnetic films instead of the permanent magnet as disclosed in JP-A-7-57223.
On the other hand, as a next generation high sensitivity MR head which takes the place of the AMR head, a spin valve head utilizing a giant magnetoresistive effect has been proposed as disclosed in JP-A-4-358310. The spin valve head comprises, as a magnetoresistive effect film, a first ferromagnetic film whose direction of magnetization is changed by a magnetic field from a magnetic recording medium, a second ferromagnetic film whose direction of magnetization is fixed, and a non-magnetic conductive film inserted between the first and second ferromagnetic films. The second ferromagnetic film is stacked on an antiferromagnetic film or a permanent magnet which serves to fix the direction of magnetization of the second ferromagnetic film. In order to enhance an output of the spin valve head, a dual spin valve head has been proposed as an application of the spin valve head as disclosed in JP-A-5-347013. The dual spin valve head comprises, as a magnetoresistive effect film, a first ferromagnetic film whose direction of magnetization is changed by a magnetic field from a magnetic recording medium, second and third ferromagnetic films whose directions of magnetization are fixed, a non-magnetic conductive film inserted between the first ferromagnetic film and the second ferromagnetic film and a non-magnetic conductive film inserted between the first ferromagnetic film and the third ferromagnetic film. The second ferromagnetic film and the third ferromagnetic film are stacked above and below the first ferromagnetic film to oppose the first ferromagnetic film, and the second and third ferromagnetic films are directly stacked on antiferromagnetic films or permanent magnet films which serve to fix the directions of magnetization of the second and third ferromagnetic films.
In those spin valve heads, since the direction of magnetization is changed by the magnetic field from the magnetic recording head in the first ferromagnetic film, it is required to maintain the first ferromagnetic film in the single magnetic domain state.
The spin valve head has been known as one which takes the place of the AMR head, but in the prior art spin valve head which uses the hard biasing system, a reproduced waveform may be distorted or a reproduced output may be decreased by a strength of the magnetic domain control layer.
For example, when a strength of the magnetic domain control layer is not enough to bring the first ferromagnetic film to the single magnetic domain state, the reproduced waveform may be distorted and the magnetic recording and reproducing apparatus may malfunction. This distortion is usually called a Barkhausen noise and it has been proved that a cause of the generation of this noise is discontinuous movement of magnetization at the ends of the first ferromagnetic film. This Barkhausen noise is easier to be generated in the spin valve head than in the AMR head. This is because, in the spin valve head, the operation is mainly conducted while the magnetization of the first ferromagnetic film is oriented laterally and in the AMR head, the operation is mainly conducted while the magnetization of the MR film is inclined to approximately 45 degrees. Namely, in the spin valve head, when leakage magnetic fields (positive and negative) of the magnetic recording medium are applied, the magnetization at the ends of the first ferromagnetic film are vertically inverted. This is because a static energy is high when the magnetization at the ends of the first ferromagnetic film is directed laterally while the strength of the magnetic domain control layer is not sufficient so that the oblique upward or oblique downward direction of magnetization is in an instable state. On the other hand, in the AMR head, since the magnetization at the ends of the first ferromagnetic film is always oriented obliquely, the discontinuous movement of the magnetization as observed in the spin valve head does not take place.
When the strength of magnetization is sufficient to a certain extent and the spacing of the electrodes of the spin valve head is reduced to increase a track density of the magnetic recording and reproducing apparatus, an output (sensitivity) per unit electrode spacing abruptly decreases. The output of the spin valve head increases basically in proportion to the electrode spacing. This is because the longer the areas in which the voltage changes are serially connected, the larger is the overall change in the voltage. However, when the electrode spacing is simply reduced in the prior art hard biasing system spin valve head, the output (sensitivity) per unit electrode spacing abruptly decreases. Particularly when the electrode spacing is reduced to 2 xcexcm or less, the sensitivity of the head is reduced to 90% or less of its inherent sensitivity. A cause for the reduction of the sensitivity is the low sensitivity at the left and right end regions of the first ferromagnetic film caused by the influence of the magnetic domain control layer stacked below the electrode. Accordingly, as the electrode spacing is reduced and the influence of the magnetic domain control layer increases, a proportion of the high sensitivity central area is reduced, and as a result, the sensitivity is reduced. Accordingly, in the prior art hard biasing system spin valve head, when the electrode spacing is simply reduced, the sensitivity is abruptly reduced and the malfunction of the magnetic recording and reproducing apparatus increases. As a result, it is difficult to increase the track density of the magnetic recording and reproducing apparatus.
Further, when the strength of the magnetic domain control layer is sufficient to a certain extent, the head output is abruptly reduced as the strength of the magnetic domain control layer increases even if the electrode spacing is kept unchanged. For example, when a longitudinal bias ratio which is a factor to indicate the strength of the magnetic domain control layer is 2, the head output is reduced to approximately 60% of its inherent output. When the magnetic domain control layer is the permanent magnet film, the longitudinal bias ratio is represented by a ratio of a product (Brxc2x7t) of a remanent magnetic flux density Br of the permanent magnet film and a film thickness t, and a product (Bsxc2x7t) of a saturation magnetic flux density Bs of the first ferromagnetic film in the spin valve head and the film thickness t. When the magnetic domain control layer is the stacked layer of the ferromagnetic films and the antiferromagnetic films, the longitudinal bias ratio is represented by a ratio of a product (Bsxc2x7t) of the saturation magnetic flux density Bs of the ferromagnetic film in the magnetic domain control layer and the film thickness t, and a product (Bsxc2x7t) of a saturation magnetic flux density Bs of the first ferromagnetic film in the spin valve head and the film thickness t.
Further, since the magnetic domain control layer is manufactured in a separate process from that of the first ferromagnetic film, the strength of the magnetic domain control layer, that is, the longitudinal bias ratio includes a variation to some extent. As a result, the head output includes a variation. Further, as described above, since the Barkhausen noise is generated if the strength of the magnetic domain control layer is insufficient, the strength of the magnetic domain control layer is set to be somewhat larger than a required value. As a result, the output is reduced.
In the prior art hard bias system spin valve head, since the head output largely depends on the strength of the magnetic domain control layer, the output is reduced and the malfunction of the magnetic recording and reproducing apparatus increases when the strength of the magnetic domain control layer is high.
It is an object of the present invention to provide a magnetoresistive effect head which can produce a high reproduced output independently from the strength of the magnetic domain control layer even if the electrode spacing is small, and a magnetic recording and reproducing apparatus using such a head.
In order to achieve the above object, according to the present invention, there is provided a magnetoresistive effect head comprising a magnetoresistive effect film having a plurality of stacked films of a dimension corresponding to a track width of a magnetic recording medium, magnetic domain control layers arranged on the opposite sides of said magnetoresistive effect film intersecting a stacking direction of the magnetoresistive effect film, and a pair of electrodes stacked on said magnetic domain control layers and electrically connected to said magnetoresistive effect film. The magnetoresistive effect film comprises a first ferromagnetic film of single layer or multi-layer having a direction of magnetization thereof changed by a magnetic field from a magnetic recording medium, a second ferromagnetic film of single layer or multi-layer having a direction of magnetization thereof fixed and a nonmagnetic conductive film inserted between the first ferromagnetic film and the second ferromagnetic film, and the second ferromagnetic film is stacked directly on an antiferromagnetic film or a permanent magnet film for fixing the direction of magnetization of the second ferromagnetic film. Portions of the pair of electrodes are stacked on the magnetoresistive effect film and a spacing of said electrodes is narrower than a width of said magnetoresistive effect film or the electrodes are arranged at positions which cause the flow of current only at a central area of the magnetoresistive effect film and the electrode spacing is not larger than 2 xcexcm. The spacing may be 0.25-1.5 xcexcm.
In the magnetoresistive effect head utilizing the giant magnetoresistive effect, when the antiferromagnetic film or the permanent magnet film for fixing the direction of magnetization is directly stacked on the second ferromagnetic film, portions of a pair of electrodes may be stacked on the antiferromagnetic film or the permanent magnet film and the electrode spacing may be smaller than a width of the magnetoresistive effect film.
Further, according to the present invention, there is provided a magnetoresistive effect head comprising a magnetoresistive effect film having a plurality of stacked films of dimension corresponding to a track width of a magnetic recording medium, magnetic domain control layers arranged on the opposite sides of the magnetoresistive effect film and a pair of electrodes stacked on the magnetic domain control layers and electrically connected to the magnetoresistive effect film. The magnetoresistive effect film comprises a first ferromagnetic film of single layer or multi-layer having a direction of magnetization thereof changed by a magnetic field from the magnetic recording medium, second and third ferromagnetic films of single layers or multilayers having a direction of magnetization thereof fixed, a first non-magnetic conductive film inserted between the first ferromagnetic film and the second ferromagnetic film and a second non-magnetic conductive film inserted between the second ferromagnetic film and the third ferromagnetic film. The first ferromagnetic film is stacked on the second ferromagnetic film and the third ferromagnetic film is stacked on the first ferromagnetic film. Antiferromagnetic films or permanent magnet films for fixing the directions of magnetization of the second and third ferromagnetic films are provided.
In the magnetoresistive effect head utilizing the giant magnetoresistive effect, when the antiferromagnetic film or the permanent magnet film for fixing the direction of magnetization is directly stacked on the third ferromagnetic film, portions of the pair of electrodes may be stacked on the antiferromagnetic film or the permanent magnet film and the electrode spacing may be smaller than the width of the magnetoresistive effect film, or the electrodes may be arranged at current supplying positions only in the central area of the magnetoresistive effect film with the electrode spacing being 2 xcexcm or less.
In the magnetoresistive effect head of the present invention, when the permanent magnet film is used as the magnetic domain control layer, the magnetic film for fixing the direction of magnetization of the second or third ferromagnetic film is preferably the antiferromagnetic film, and when the stacked layer of the antiferromagnetic film and the soft magnetic film is used as the magnetic domain control layer, the magnetic film for fixing the direction of magnetization of the second or third ferromagnetic film is preferably the antiferromagnetic film or the permanent magnet. The former case is more preferable.
The width of the ferromagnetic effect film is preferably the spacing of the pair of electrodes plus 0.5-4 xcexcm.
The position of the electrode end which defines the electrode spacing of the pair of electrodes is preferably in a range of 0.25-2 xcexcm from the widthwise ends of the magnetoresistive effect film.
Further, the electrode spacing of the pair of electrodes may be set to 2 xcexcm or less, preferably 0.25-1.5 xcexcm.
The magnetoresistive effect head of the present invention may be used as a reproducing head and applied to the following apparatus.
(1) A magnetic recording and reproducing apparatus comprising a magnetic recording medium for magnetically recording information, a reproducing head for transducing a change in a magnetic field leaked from the magnetic recording medium to an electrical signal and a reproduction circuit for processing the electrical signal from the reproducing head.
(2) A magnetic reproducing apparatus comprising a magnetic recording medium for magnetically recording information, a recording head for generating a magnetic field corresponding to an electrical signal and recording information represented by the magnetic field on a magnetic recording medium, a reproducing head for transducing a change in a magnetic field leaked from the magnetic recording medium to an electrical signal and a reproduction circuit for processing the electrical signal from the reproducing head.
(3) A disk array system comprising a plurality of above magnetic recording and reproducing apparatus and a controller for controlling the plurality of apparatus. In accordance with the means described above, the opposite ends of each electrode are arranged farther in than the widthwise end positions of the magnetoresistive effect film, so no substantial current flows to the widthwise ends of the magnetoresistive effect film and a current flows only in the central area which is hard to be influenced by the magnetic field from the magnetic domain control layer. Accordingly, even if the strength of the magnetic domain control layer is not sufficiently high, the generation of the Barkhausen noise from the magnetoresistive effect film is suppressed. Further, even if the strength of the magnetic domain control film layer is high, a high output may be maintained. Further, even if the electrode width is reduced, a high sensitivity output is maintained with a small read spread so that a high track density is attained.
In accordance with the present invention, since the electrode spacing is smaller than the width of the magnetoresistive effect film and the current flows only in the central area of the magnetoresistive effect film, the generation of the Barkhausen noise is suppressed even if the strength of the magnetic domain control layer is not sufficiently high, and even if the strength of the magnetic domain control layer is sufficiently high, the variation in the output may be suppressed to a low value. Further, even if the electrode spacing is small, a high sensitivity is attained with a small read spread, and the high track density is attained.
When the head of the present invention is used in the magnetic reproducing apparatus or the magnetic recording and reproducing apparatus, the malfunction may be reduced.